JP2015033767A - Method for manufacturing conductive rubber foam roller, conductive rubber form roller, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a conductive rubber foam roller, by which no cracks by abnormal foaming are present in a cylindrical body after foaming, and thereby, peeling or denting is prevented in a succeeding polishing process, and to provide a conductive rubber foam roller manufactured by the above method, and an image forming apparatus in which the conductive rubber foam roller is assembled.SOLUTION: The method for manufacturing a conductive rubber foam roller includes a step of passing a long cylindrical body 7 that is prepared by continuously extrusion-molding a rubber composition, without cutting, through a microwave crosslinking device 8 and then a hot blow crosslinking device 9. The rubber composition is extrusion-molded, foamed and crosslinked in such a manner that a thickness deviation degree represented by a ratio T/Tof the largest thickness Tto the smallest thickness Tin a radial direction on a cross section of the cylinder immediately after passing through the hot blow crosslinking device 9, is 1.3 or less. A conductive rubber foam roller is manufactured through the above steps. The conductive rubber foam roller is assembled in an image forming apparatus.

Description

  The present invention relates to a method for producing a conductive foam rubber roller, a conductive foam rubber roller produced by such a production method, and an image forming apparatus incorporating the conductive foam rubber roller.

For example, in an image forming apparatus using electrophotography such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, or a complex machine of these, paper (plastic film such as an OHP film) is roughly processed through the following steps. An image is formed on the surface of the same.
First, the surface of the photoconductive photoconductor is exposed in a uniformly charged state, and an electrostatic latent image corresponding to the formed image is formed on the surface (charging step → exposure step).

Next, the toner, which is minute colored particles, is brought into contact with the surface of the previous photoreceptor in a state where the toner is charged to a predetermined potential. Then, the toner is selectively attached to the surface of the photoconductor according to the potential pattern of the electrostatic latent image, and the electrostatic latent image is developed into a toner image (development process).
Next, the toner image is transferred to the surface of the paper (transfer process) and further fixed (fixing process), whereby an image is formed on the surface of the paper.

In the transfer process, the toner image formed on the surface of the photoconductor is not only transferred directly to the surface of the paper, but also transferred to the surface of the image carrier (primary transfer process) and then re-transferred to the surface of the paper. In some cases, the image is transferred (secondary transfer process).
Further, a series of image formation is completed by removing the toner remaining on the surface of the photoreceptor after the transfer (cleaning process).

Among the above-described processes, the charging process, the developing process, the transferring process, and the cleaning process of the photosensitive member are made of a rubber cylindrical body that is provided with conductivity and foamed according to each application. Conductive foam rubber rollers that are in contact with the surface of the body are widely used.
As a method for producing a conductive foam rubber roller, the following continuous methods are known (Patent Documents 1 to 4, etc.).

That is, a rubber composition having electrical conductivity, crosslinkability, and foamability is continuously extruded into a cylindrical shape using an extruder, and the extruded cylindrical body is not cut and remains long. It is continuously foamed and cross-linked by passing through a wave cross-linking apparatus and then a hot air cross-linking apparatus.
Next, it is cut to a predetermined length and subjected to secondary cross-linking, and the shaft is inserted into and fixed to the through hole of the cylinder, and the outer peripheral surface is polished to a predetermined outer diameter.

JP 2007-322729 A JP 2008-90236 A JP 2010-145920 A JP 2010-217521 A

One of the problems when manufacturing a conductive foam rubber roller by the continuous method is that abnormal foaming occurs locally inside the cylindrical body during foaming, and accompanying this, cracking occurs inside the cylindrical body after foaming. To be inherent.
If a crack is present inside the cylindrical body, the crack may reach the outer peripheral surface of the conductive foam rubber roller by subsequent polishing, and the cracked portion may peel off. Even when the crack does not reach the outer peripheral surface, the outer peripheral surface may be depressed due to the effect of the internal crack.

And when such peeling and a hollow arise, there exists a problem of producing the dimensional accuracy and hardness of the outer diameter of a conductive rubber roller.
An object of the present invention is to provide a production method capable of producing a conductive foamed rubber roller that does not cause peeling or dents in a subsequent polishing step because cracks due to abnormal foaming do not exist inside the tubular body after foaming. There is. Another object of the present invention is to provide a conductive foamed rubber roller manufactured by such a manufacturing method and an image forming apparatus incorporating the conductive foamed rubber roller.

The present invention relates to a microwave crosslinking apparatus in which a rubber composition having conductivity, crosslinkability, and foamability is continuously extruded into a cylindrical shape, and then the extruded cylindrical body is long without being cut. Then, a manufacturing method for producing a conductive foamed rubber roller through a process of continuously foaming and cross-linking by passing through a hot-air cross-linking device, wherein in the process, the radial maximum thickness T _max of the cross section immediately after foaming minimum thickness as thickness deviation, expressed by the ratio T _{max /} T _min and T _min is 1.3 or less, the rubber composition of the extrusion, foaming, and conductive, characterized in that crosslinking and It is a manufacturing method of a foam rubber roller.

According to the inventor's study, a cylindrical body in which local abnormal foaming that causes cracking in the foaming process is uneven in thickness in the radial direction, that is, uneven in thickness.
On the other hand, the unevenness degree represented by the ratio T _max / T _min of the radial maximum thickness T _max and the minimum thickness T _min of the cross section immediately after passing through the hot-air crosslinking apparatus is 1.3 or less. When extrusion, foaming, and cross-linking of a cylindrical body, abnormal foaming locally occurs inside the cylindrical body at the time of foaming, and accordingly, cracks are inherent in the cylindrical body after foaming. Can be prevented.

Therefore, it is possible to manufacture a conductive foamed rubber roller that does not cause peeling or dents in the subsequent polishing process and does not affect the dimensional accuracy and hardness of the outer diameter.
In order to make the thickness deviation within such a range, the cylindrical body is extruded so that the thickness is as uniform as possible, and the extruded cylindrical body is foamed and crosslinked as evenly as possible.

In particular, it is important to extrude the cylindrical body so that the thickness is as uniform as possible in order to reduce the thickness deviation.
To that end, in extrusion molding, an extruder having a die whose opening shape is circular, and a core disposed in the die and having a circular cross-sectional shape in the same plane as the opening of the die. And the maximum and minimum distances in the radial direction of the opening at a plurality of locations in the circumferential direction of the opening between the opening of the base and the cross section of the core in the same plane as the opening. From the value, formula (1):

The rubber composition is extruded into a cylindrical shape through an annular gap between the base and the core while the base and the core are aligned so that the error required by the step is within 10%. It is preferable to mold.
With this setting, the thickness deviation of the cylindrical body before foaming that is extruded through the annular gap between the die and the core can be reduced as much as possible, and it is continuously passed through the microwave crosslinking apparatus and then the hot-air crosslinking apparatus. The thickness of the cylindrical body immediately after passing through the hot-air cross-linking device is 1.3 or less, and abnormal foaming is locally generated inside the cylindrical body at the time of foaming. Thus, it is possible to more reliably prevent cracks from being present inside the cylindrical body after foaming.

The present invention is a conductive foamed rubber roller manufactured by the manufacturing method of the present invention.
According to the present invention, based on the manufacturing method of the present invention described above, it is possible to obtain a conductive foamed rubber roller that does not have peeling or dents that affect dimensional accuracy and hardness.
The present invention also provides an image forming apparatus incorporating the conductive foam rubber roller of the present invention.

  According to the present invention, an image excellent in image characteristics of a formed image can be obtained by incorporating the conductive foamed rubber roller of the present invention having no peeling or depression affecting the dimensional accuracy and hardness as described above, for example, as a transfer roller. A forming device can be obtained.

  According to the present invention, since there is no crack due to abnormal foaming inside the tubular body after foaming, it is possible to provide a production method capable of producing a conductive foam rubber roller that does not cause peeling or dents in the subsequent polishing step. . Further, according to the present invention, it is possible to obtain a conductive foamed rubber roller manufactured by such a manufacturing method and an image forming apparatus incorporating the conductive foamed rubber roller.

It is a block diagram explaining an example of the process of extrusion-molding, foaming, and bridge | crosslinking a rubber composition among the manufacturing methods of the conductive foam rubber roller of this invention. It is a perspective view which shows an example of the electroconductive foamed rubber roller of this invention manufactured by the manufacturing method of this invention including the process of FIG. It is sectional drawing for demonstrating how to obtain | require the radial thickness deviation in the cylindrical body just after passing the hot-air bridge | crosslinking apparatus obtained through the process of FIG. It is a perspective view explaining an example of a die used for extrusion molding of a rubber composition, and an inside core among processes of Drawing 1. It is a front view for demonstrating how to obtain | require the difference | error of the distance of radial direction in a nozzle | cap | die and a center core of the example of FIG.

<< Method of manufacturing conductive foam rubber roller, and conductive foam rubber roller >>
FIG. 1 is a block diagram for explaining an example of steps of extrusion molding, foaming, and crosslinking of a rubber composition in the method for producing a conductive foam rubber roller of the present invention. FIG. 2 is a perspective view showing an example of the conductive foam rubber roller of the present invention manufactured by the manufacturing method of the present invention including the process of FIG. Further, FIG. 3 is a cross-sectional view for explaining how to obtain the radial thickness deviation in the tubular body immediately after passing through the hot-air bridging apparatus obtained through the process of FIG.

Referring to FIG. 2, a conductive foam rubber roller 1 of this example is formed in a single-layered cylindrical shape from a rubber composition having conductivity, crosslinkability, and foamability. 3 is inserted and fixed, and the outer peripheral surface 4 is polished.
Referring to FIG. 1, a manufacturing apparatus 5 used in the manufacturing method of this example cuts an extruder 6 for continuously extruding a rubber composition into a cylindrical shape and an extruded cylindrical body 7. In order to take up the microwave bridging device 8, the hot air bridging device 9, and the tubular body 7 arranged at a constant speed in the course of continuous conveyance by a conveyor or the like (not shown) without being long. The take-up machine 10 is provided.

In the production method of the present invention, first, a rubber composition having conductivity, crosslinkability, and foamability, which is the basis of the cylindrical body 7 is blended in a predetermined ratio with components such as a rubber component and a foaming agent. The continuous tubular body 7 is continuously extruded by operating the extruder 6 while continuously supplying the ribbon-shaped one or the like to the extruder 6.
Next, while the extruded cylindrical body 7 is continuously conveyed at a constant speed by the conveyor and the take-up machine 10, the microwave is first irradiated by passing through the microwave bridging device 8, and the cylindrical body The rubber composition forming 7 is crosslinked to a certain degree of crosslinking. Moreover, the inside of the microwave bridge | crosslinking apparatus 8 can be heated to fixed temperature, and a foaming agent can be decomposed | disassembled and foamed a rubber composition with bridge | crosslinking.

Subsequently, the hot air is passed through the hot air cross-linking device 9 while continuing the conveyance, and the foaming agent is decomposed to further foam the rubber composition, and the rubber composition is cross-linked to a predetermined degree of cross-linking.
Referring to FIG. 3, in the manufacturing method of the present invention, in the step of FIG. 1, through-hole 11 and outer peripheral surface 12 of tubular body 7 in the cross section of tubular body 7 immediately after passing through hot air bridging device 9. radial distance, that is, the maximum value of the radial thickness (maximum _{thickness) T max} and the minimum value (minimum _thickness) thickness deviation represented by the ratio _T max _{/ T min} and _{T min} is 1 between. In this step, the rubber composition is extruded, foamed, and crosslinked so as to be 3 or less.

If it does so, it can prevent that abnormal foaming locally arises in the inside of the cylindrical body 7 at the time of foaming, and that the crack exists in the inside of the cylindrical body 7 after foaming in connection with it.
The lower limit of the uneven thickness is 1. In other words, it is most ideal that no uneven thickness occurs.
However, since the substantially equivalent effect can be obtained if the unevenness degree is 1.3 or less, the unevenness degree is in the range of 1 or more and 1.3 or less in consideration of the productivity of the conductive foam rubber roller 1. What is necessary is just to carry out extrusion molding, foaming, and bridge | crosslinking, adjusting so that it may become.

However, in order to make the conductive foamed rubber roller 1 have a predetermined outer diameter and suppress the deflection of the outer peripheral surface 4, the amount of the rubber composition used is reduced by reducing the polishing amount when polishing the outer peripheral surface 4 as much as possible. In consideration of this, the thickness deviation is preferably 1.26 or less.
In order to adjust the thickness deviation within the above range, the cylindrical body 7 is extruded so that the thickness is as uniform as possible, and the extruded cylindrical body 7 is foamed and crosslinked as evenly as possible. Just do it.

In particular, it is important to extrude the cylindrical body 7 so that the thickness is as uniform as possible in order to reduce the thickness deviation.
FIG. 4 is a perspective view for explaining an example of a die and a core used for extrusion molding of a rubber composition in the process of FIG. FIG. 5 is a front view for explaining how to determine the radial distance error between the base and the core in the example of FIG.

Referring to FIG. 4, in order to extrude the rubber composition into a cylindrical shape, in this example, the base 14 having a circular shape of the opening 13 and the opening of the base 14 are provided in the base 14. Are used in combination with a core 16 having a circular cross section 15 in the same plane.
Among these, the center core 16 is formed in a conical shape, and a conical shaft 17 indicated by an alternate long and short dash line in the drawing coincides with the extrusion direction E of the cylindrical body 7 (indicated by a solid arrow in the drawing), and the apex of the cone. 18 is directed in the extrusion direction, and the apex 18 is disposed in the base 14 in a state of protruding from the opening 13 of the base 14 in the extrusion direction.

  In order to extrude the cylindrical body 7 having a uniform thickness as much as possible by combining the base 14 and the center core 16, the opening 13 of the base 14 and the cross section 15 of the center core 16 in the same plane as the opening 13. 14 so that the error determined by the above equation (1) is within 10% from the maximum value and the minimum value of the radial distance at a plurality of locations in the circumferential direction of the opening 13 between The rubber composition is preferably extruded into a cylindrical shape through an annular gap between the die 14 and the core 16 in a state where the core and the core 16 are aligned.

For the adjustment of the error, for example, it is preferable to use a pressing amount adjusting function in a fixing mechanism for pressing and fixing the base 14 with respect to the shaft 17 of the center core 16 from above, below, right and left by four screws. That Referring to FIG. 5, the press amount of the four directions of the fixing mechanism, not shown, corresponding to such four directions of the fixing mechanism, the maximum value and the minimum in the distance d ₁ to d ₄ four directions of the shaft 17 From the value, adjustment is made so that the error obtained by the equation (1) is within 10%.

  Then, the thickness deviation of the tubular body 7 before foaming that is extruded through the annular gap between the base 14 and the inner core 16 can be made as small as possible, and the microwave bridging device 8 and then the hot-air bridging device 9 are passed. The uneven thickness of the tubular body 7 immediately after passing through the hot air bridging device 9 that has been continuously foamed and crosslinked is set to 1.3 or less, and abnormal foaming is locally generated inside the tubular body 7 at the time of foaming. It is possible to more reliably prevent the occurrence of cracks and the occurrence of cracks inside the cylindrical body 7 after foaming.

It should be noted that the lower limit of the error obtained by the equation (1) is ideally preferably 0%. However, if the error is within 10%, almost the same effect can be obtained. Therefore, considering the productivity of the conductive foam rubber roller 1 by simplifying the preparation effort, the error is 0% or more and 10% or less. It is preferable to perform extrusion molding while adjusting so as to be in the above range.
Further, it is also effective to foam and crosslink the extruded cylindrical body 7 as uniformly as possible, as described above, so that the uneven thickness described above is 1.3 or less.

Since the microwave crosslinking apparatus 8 and the hot air crosslinking apparatus 9 used in the continuous method are generally designed in consideration of such points, the extruded cylindrical body 7 is usually left as it is. You can just pass through the device.
However, the entire cylindrical body 7 may be twisted in the course of conveyance so that the microwave irradiation dose and the degree of heating can be made more uniform, and foamed and crosslinked evenly. Good.

Thereafter, the foamed and cross-linked cylindrical body 7 is cut to a predetermined length and, if necessary, heated in a hot air oven or the like to be secondary cross-linked, and then into the through-hole 2 as shown in FIG. The shaft 3 is inserted and fixed, and the outer peripheral surface 4 is polished, whereby the conductive foam rubber roller 1 is manufactured which is electrically joined to the shaft 3 and mechanically fixed as shown in FIG. Is done.
Polishing can be performed at any time, but in the state of FIG. 2 where the shaft 3 is cut and inserted and fixed, polishing is performed while rotating around the shaft 3 to improve workability. In addition, it is preferable for suppressing the deflection of the outer peripheral surface 4.

At this time, according to the present invention, as described above, the thickness deviation of the cylindrical body 7 is 1.3 or less, and cracks due to abnormal foaming are not inherent in the cylindrical body 7, The conductive foamed rubber roller 1 that does not cause peeling or dent due to polishing and does not affect the dimensional accuracy and hardness of the outer diameter can be manufactured.
Further, according to the present invention, there is an advantage that the productivity can be improved and the production cost of the conductive foam rubber roller 1 can be reduced by carrying out the continuous method.

The shaft 3 is integrally formed of a metal such as aluminum, an aluminum alloy, or stainless steel.
Such a shaft 3 may be electrically joined to the conductive foamed rubber roller 1 and mechanically fixed by press-fitting a shaft having an outer diameter larger than the inner diameter of the through-hole 2, or a conductive heat. The conductive foam rubber roller 1 may be electrically bonded and mechanically fixed via a curable adhesive.

In the latter case, for example, when the thermosetting adhesive is cured by heating in a hot air oven, the conductive foamed rubber roller 1 may be secondarily crosslinked at the same time.
The details of the microwave cross-linking device 8 and the hot air cross-linking device 9 are as described in, for example, Patent Documents 1 to 3 described above.
The conductive foam rubber roller 1 can be used by being incorporated in an image forming apparatus using electrophotography, for example, as a charging roller, a developing roller, a transfer roller, or the like.

The conductive foamed rubber roller 1 is measured under a normal temperature and humidity environment at a temperature of 23 ° C. and a relative humidity of 55% according to the measurement method described in Japan Rubber Association Standard SRIS 0101 “Physical Test Method for Expanded Rubber”. The Asker C-type hardness measured with a 9N load applied is preferably 50 ° or less.
The conductive foamed rubber roller 1 having an Asker C-type hardness exceeding this range lacks flexibility. For example, when used as a transfer roller, the conductive foam rubber roller 1 has an effect of ensuring a wide nip width to improve toner transfer efficiency and photosensitivity. The effect of reducing damage to the body may not be obtained.

In order to adjust Asker C-type hardness, for example, the type and amount of each component constituting the rubber composition may be adjusted.
<Rubber composition>
The rubber composition used as the base of the conductive foamed rubber roller 1 can be extruded into a cylindrical shape by using an extruder 6 and is foamed and cross-linked when passed through the microwave cross-linking device 8 and the hot-air cross-linking device 9. It is possible to use a rubber composition having any foaming property and cross-linking property and having any conductivity according to the use of the conductive foamed rubber roller 1.

In particular, a rubber composition imparted with ionic conductivity using an ionic conductive rubber also serving as a rubber component is preferable as the conductivity imparting agent.
<Rubber>
As the rubber component, it is preferable to use an ion conductive rubber and a crosslinkable rubber in combination.
(Ion conductive rubber)
As the ion conductive rubber, epichlorohydrin rubber is preferable.

  Examples of the epichlorohydrin rubber include epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide binary copolymer (ECO), epichlorohydrin-propylene oxide binary copolymer, epichlorohydrin-allyl glycidyl ether binary copolymer, epichlorohydrin-ethylene oxide- 1 type or 2 types, such as allylic glycidyl ether terpolymer (GECO), epichlorohydrin-propylene oxide-allyl glycidyl ether terpolymer, and epichlorohydrin-ethylene oxide-propylene oxide-allyl glycidyl ether quaternary copolymer The above is mentioned.

As the epichlorohydrin rubber, among the examples, a copolymer containing ethylene oxide, particularly ECO and / or GECO is preferable.
In both copolymers, the ethylene oxide content is preferably 30 mol% or more, particularly preferably 50 mol% or more, and more preferably 80 mol% or less.
Ethylene oxide serves to lower the roller resistance value of the entire conductive foam rubber roller 1. However, when the ethylene oxide content is less than this range, such a function cannot be obtained sufficiently, and the roller resistance value may not be sufficiently reduced.

On the other hand, when the ethylene oxide content exceeds the range, crystallization of ethylene oxide occurs and the segmental movement of the molecular chain is hindered, so that the roller resistance value tends to increase. Further, there is a possibility that the hardness of the conductive foamed rubber roller 1 after foaming and cross-linking increases, or the viscosity of the rubber composition before cross-linking increases during heating and melting.
The epichlorohydrin content in ECO is the remaining amount of ethylene oxide content. That is, the epichlorohydrin content is preferably 20 mol% or more, preferably 70 mol% or less, and particularly preferably 50 mol% or less.

Further, the allylic glycidyl ether content in GECO is preferably 0.5 mol% or more, particularly preferably 2 mol% or more, more preferably 10 mol% or less, and particularly preferably 5 mol% or less.
The allyl glycidyl ether itself functions to secure a free volume as a side chain, thereby suppressing the crystallization of ethylene oxide and reducing the roller resistance value of the conductive foam rubber roller 1. However, when the allyl glycidyl ether content is less than this range, such a function cannot be obtained, so that the roller resistance value may not be sufficiently reduced.

  On the other hand, since allyl glycidyl ether functions as a crosslinking point during GECO crosslinking, when the allyl glycidyl ether content exceeds the range, the GECO crosslinking density becomes high and the molecular chain segmental movement is hindered. The resistance value tends to increase. Further, the elongation, 100% modulus, fatigue characteristics, bending resistance, etc. of the conductive foam rubber roller 1 may be reduced.

The epichlorohydrin content in GECO is the remaining amount of ethylene oxide content and allyl glycidyl ether content. That is, the epichlorohydrin content is preferably 10 mol% or more, particularly 19.5 mol% or more, preferably 69.5 mol% or less, particularly preferably 60 mol% or less.
GECO includes a modified product obtained by modifying epichlorohydrin-ethylene oxide copolymer (ECO) with allyl glycidyl ether in addition to the above-described copolymer in the narrow sense obtained by copolymerization of the three types of monomers. Any GECO can be used in the present invention.

The blending ratio of epichlorohydrin rubber is preferably 5 parts by mass or more, particularly 10 parts by mass or more, and preferably 40 parts by mass or less, particularly 30 parts by mass or less, in 100 parts by mass of the total amount of rubber.
If the blending ratio is less than this range, the conductive foamed rubber roller 1 may not be provided with good ionic conductivity.

On the other hand, when it exceeds the range, the blending ratio of the crosslinkable rubber is relatively reduced, and there is a possibility that the effect of blending various crosslinkable rubbers described below cannot be sufficiently obtained.
(Crosslinkable rubber)
Examples of the crosslinkable rubber include styrene butadiene rubber (SBR) and / or acrylonitrile butadiene rubber (NBR). These rubbers have good crosslinkability, and can impart good rubber elasticity and flexibility to the foamed and foamed conductive foamed rubber roller 1.

Further, when ethylene propylene diene rubber (EPDM) is further blended as the crosslinkable rubber, the resistance of the conductive foam rubber roller 1 to ozone generated in the image forming apparatus can be improved.
(SBR, NBR)
As the SBR, any of various SBRs synthesized by copolymerizing styrene and 1,3-butadiene by various polymerization methods such as an emulsion polymerization method and a solution polymerization method can be used. In addition, as SBR, there are an oil-extended type in which flexibility is adjusted by adding an extending oil and a non-oil-extended type in which flexibility is not added, either of which can be used.

Furthermore, as the SBR, any of SBR of high styrene type, medium styrene type, and low styrene type classified by styrene content can be used. Various physical properties of the conductive foam rubber roller 1 can be adjusted by changing the styrene content and the degree of crosslinking.
One or more of these SBRs can be used.
As NBR, any of low nitrile NBR, medium nitrile NBR, medium high nitrile NBR, high nitrile NBR, and extremely high nitrile NBR classified by acrylonitrile content can be used. One or more of these NBRs can be used.

Furthermore, SBR and NBR can be used together.
The blending ratio of SBR and / or NBR is preferably 40 parts by mass or more, particularly 60 parts by mass or more, and particularly 90 parts by mass or less, particularly 80 parts by mass or less, in 100 parts by mass of the total amount of rubber. preferable.
When the blending ratio is less than this range, the effect of imparting good crosslinkability to the rubber composition described above by using SBR and / or NBR, and the conductive foamed rubber roller 1 after foaming and crosslinking are used. There is a possibility that the effect of imparting good rubber elasticity and flexibility cannot be obtained sufficiently.

On the other hand, when it exceeds the range, the blending ratio of EPDM is relatively reduced, and there is a possibility that good ozone resistance cannot be imparted to the conductive foamed rubber roller 1. Further, the blending ratio of epichlorohydrin rubber is relatively decreased, and there is a possibility that good ionic conductivity cannot be imparted to the conductive foam rubber roller 1.
In addition, a mixing | blending ratio is a mixing | blending ratio of SBR itself as solid content contained in SBR of the said oil-extended type when using an oil-extended type thing as SBR. Moreover, when using SBR and NBR together, it is the total blending ratio.
(EPDM)
As EPDM, any of various EPDMs in which a double bond is introduced into the main chain by adding a small amount of a third component (diene component) to ethylene and propylene can be used.

As EPDM, various products are provided depending on the kind and amount of the third component. Representative examples of the third component include ethylidene norbornene (ENB), 1,4-hexadiene (1,4-HD), dicyclopentadiene (DCP), and the like. A Ziegler catalyst is generally used as the polymerization catalyst.
The blending ratio of EPDM is preferably 5 parts by mass or more, more preferably 40 parts by mass or less, and particularly preferably 20 parts by mass or less, in 100 parts by mass of the total rubber content.

If the blending ratio is less than this range, there is a possibility that good ozone resistance cannot be imparted to the conductive foamed rubber roller 1.
On the other hand, when exceeding the range, the blending ratio of SBR and / or NBR is relatively reduced, and by blending these rubbers, the effect of imparting good crosslinkability to the rubber composition, foaming, Further, there is a possibility that the effect of imparting good rubber elasticity and flexibility to the conductive foamed rubber roller 1 after crosslinking may not be sufficiently obtained. Further, the blending ratio of epichlorohydrin rubber is relatively decreased, and there is a possibility that good ionic conductivity cannot be imparted to the conductive foam rubber roller 1.

(Other rubber)
As a rubber component, polar rubber such as chloroprene rubber (CR), butadiene rubber (BR), acrylic rubber (ACM) or the like can be further blended to finely adjust the roller resistance value of the conductive foam rubber roller 1.
<Foaming component>
The rubber composition is blended with a foaming component for foaming the rubber composition.

As such a foaming component, only a foaming agent that can be decomposed by heating and generate a gas to foam the rubber composition is a ratio of 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the total amount of rubber. It is preferable to use or use together the foaming agent of the said quantity, and the foaming adjuvant of 5 mass parts or less per 100 mass parts of total amounts of rubber | gum.
As a foaming component, excluding the foaming aid that lowers the decomposition temperature of the foaming agent to reduce the cell diameter of the foamed cell, that is, it does not contain any foaming aid and decomposes by heating to generate gas. Even if only the foaming agent is used or the foaming aid is blended, the foamed cell diameter of the entire conductive foamed rubber roller 1 can be reduced by blending the blending ratio limited to the range described above. Can be big.

  In addition, the above-described abnormal foaming is suppressed by setting the blending ratio of the foaming agent within this range, the cylindrical body 7 is foamed well, and the outer peripheral surface 4 and the inner peripheral surface after foaming and cross-sectional shape are cross-linked. The conductive foam rubber roller 1 can be manufactured with a uniform circular shape as much as possible and with the distribution of the foamed cells made as uniform as possible to reduce hardness and conductivity unevenness.

In consideration of further improving this effect, the blending ratio of the foaming agent is preferably 1.5 parts by mass or more and preferably 8 parts by mass or less per 100 parts by mass of the total amount of rubber. Most preferably, no foaming aid is blended.
Examples of the blowing agent include 1 such as azodicarbonamide (H ₂ NOCN = NCONH ₂ , ADCA), 4,4′-oxybis (benzenesulfonylhydrazide) (OBSH), N, N-dinitrosopentamethylenetetramine (DPT) and the like. A seed | species or 2 or more types is mentioned.

Moreover, urea is mentioned as a foaming adjuvant.
<Crosslinking component>
In the rubber composition, a crosslinking component for crosslinking the rubber component is blended. Examples of the crosslinking component include a crosslinking agent and an accelerator.
Among these, examples of the crosslinking agent include one or more of sulfur-based crosslinking agents, thiourea-based crosslinking agents, triazine derivative-based crosslinking agents, peroxide-based crosslinking agents, various monomers, and the like. Of these, sulfur-based crosslinking agents are preferred.

Examples of sulfur-based crosslinking agents include powdered sulfur and organic sulfur-containing compounds. Among these, examples of the organic sulfur-containing compound include tetramethylthiuram disulfide and N, N-dithiobismorpholine. In particular, sulfur such as powdered sulfur is preferred.
The blending ratio of sulfur is preferably 0.2 parts by mass or more, particularly 1 part by mass or more, preferably 5 parts by mass or less, particularly 3 parts by mass or less, per 100 parts by mass of the total amount of rubber.

  If the blending ratio is less than this range, the crosslinking rate of the rubber composition as a whole becomes slow, and the time required for crosslinking becomes long, and the productivity of the conductive foamed rubber roller 1 may be lowered. Further, if the range is exceeded, there is a possibility that the compression set of the foamed and crosslinked conductive foamed rubber roller 1 becomes large, or excessive sulfur blooms on the outer peripheral surface 4 of the conductive foamed rubber roller 1.

Examples of the accelerator include inorganic accelerators such as slaked lime, magnesia (MgO), and resurge (PbO), and one or more organic accelerators.
Examples of the organic accelerator include guanidine accelerators such as di-o-tolylguanidine, 1,3-diphenylguanidine, 1-o-tolylbiguanide, dicatechol borate di-o-tolylguanidine salt; 2-mercapto Thiazole accelerators such as benzothiazole and di-2-benzothiazyl disulfide; sulfenamide accelerators such as N-cyclohexyl-2-benzothiazylsulfenamide; tetrametherthiuram monosulfide, tetramethylthiuram One type or two or more types of thiuram accelerators such as disulfide, tetraethylthiuram disulfide, and dipentamethylene thiuram tetrasulfide;

As the accelerator, one or more of the optimum accelerators may be selected from the various accelerators according to the type of the crosslinking agent to be combined. For example, when sulfur is used as a crosslinking agent, it is preferable to select and use a thiuram accelerator and / or a thiazole accelerator as an accelerator.
Moreover, since the acceleration | stimulation mechanism of a crosslinking agent changes with kinds, it is preferable to use 2 or more types together. The blending ratio of the individual accelerators used in combination can be arbitrarily set, but is preferably 0.1 parts by mass or more, particularly preferably 0.5 parts by mass or more per 100 parts by mass of the total amount of rubber. Hereinafter, it is particularly preferably 6 parts by mass or less.

As the cross-linking component, an accelerator aid may be further blended.
Examples of the acceleration aid include one or more metal compounds such as zinc oxide; fatty acids such as stearic acid, oleic acid, and cottonseed fatty acid; and other conventionally known acceleration aids.
The blending ratio of the accelerator aid can be appropriately set according to the kind and combination of the rubber component, the kind and combination of the crosslinking agent and accelerator, and the like.

<Others>
You may mix | blend various additives with a rubber composition further as needed. Examples of such additives include acid acceptors, plastic components (plasticizers, processing aids, etc.), deterioration inhibitors, fillers, scorch inhibitors, ultraviolet absorbers, lubricants, pigments, antistatic agents, flame retardants, Examples thereof include a compatibilizer, a nucleating agent, and a co-crosslinking agent.

The acid acceptor functions to prevent the chlorine-based gas generated from the epichlorohydrin rubber during the crosslinking of the rubber component from remaining in the conductive foamed rubber roller 1, thereby inhibiting crosslinking and contamination of the photoreceptor.
As the acid acceptor, various substances acting as an acid acceptor can be used. However, hydrotalcite or magsarat is preferable because of excellent dispersibility, and hydrotalcite is particularly preferable.

Further, when hydrotalcites or the like are used in combination with magnesium oxide or potassium oxide, a higher acid receiving effect can be obtained, and contamination of the photoreceptor can be prevented more reliably.
The blending ratio of the acid acceptor is preferably 0.2 parts by mass or more, particularly 0.5 parts by mass or more, preferably 5 parts by mass or less, particularly 3 parts by mass or less, per 100 parts by mass of the total amount of rubber. preferable.
If the blending ratio is less than this range, the effect of containing the acid acceptor may not be sufficiently obtained. Moreover, when exceeding a range, there exists a possibility that the hardness of the conductive foamed rubber roller 1 after foaming and bridge | crosslinking may rise.

Examples of the plasticizer include various plasticizers such as dibutyl phthalate (DBP), dioctyl phthalate (DOP), and tricresyl phosphate, and various waxes such as polar wax. Examples of the processing aid include fatty acids such as stearic acid.
The blending ratio of these plastic components is preferably 5 parts by mass or less per 100 parts by mass of the total amount of rubber. For example, when used in an image forming apparatus, it is for preventing contamination of a functional substance.

Examples of the deterioration preventing agent include various antiaging agents and antioxidants.
Among these, the antioxidant functions to reduce the environmental dependency of the roller resistance value of the conductive foam rubber roller 1 and to suppress an increase in the roller resistance value during continuous energization. As an antioxidant, for example, nickel diethyldithiocarbamate [Nocrak (registered trademark) NEC-P manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.], nickel dibutyldithiocarbamate [Nocrack NBC manufactured by Ouchi Shinsei Chemical Industrial Co., Ltd.] Etc.

Examples of the filler include one or more of zinc oxide, silica, carbon, carbon black, clay, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, and the like.
By blending the filler, the mechanical strength of the conductive foamed rubber roller 1 can be improved.
Further, it is possible to impart electronic conductivity to the conductive foamed rubber roller 1 by using conductive carbon black as a filler.

In particular, as the filler, silica or carbon black, particularly carbon black, which functions as a rubber reinforcing material and is excellent in the effect of improving the tensile properties of the conductive foam rubber roller 1 is preferable.
The blending ratio of carbon black is preferably 5 parts by mass or more per 100 parts by mass of the total amount of rubber, and is preferably 50 parts by mass or less, particularly preferably 30 parts by mass or less.

Examples of the scorch inhibitor include one or more of N-cyclohexylthiophthalimide, phthalic anhydride, N-nitrosodiphenylamine, 2,4-diphenyl-4-methyl-1-pentene, and the like. . N-cyclohexylthiophthalimide is particularly preferable.
The blending ratio of the scorch inhibitor is preferably 0.1 parts by mass or more per 100 parts by mass of the total amount of rubber, and is preferably 5 parts by mass or less, particularly preferably 1 part by mass or less.

The co-crosslinking agent refers to a component that itself has a function of crosslinking and also having a function of crosslinking the rubber component to polymerize the whole.
Examples of co-crosslinking agents include methacrylic acid esters, or ethylenically unsaturated monomers represented by metal salts of methacrylic acid or acrylic acid, polyfunctional polymers using functional groups of 1,2-polybutadiene, 1 type, or 2 or more types, such as dioxime, is mentioned.

Among these, as the ethylenically unsaturated monomer, for example
(a) monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid,
(b) dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid,
(c) esters or anhydrides of unsaturated carboxylic acids of (a) (b),
(d) a metal salt of (a) to (c),
(e) aliphatic conjugated dienes such as 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene,
(f) aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, ethylvinylbenzene, divinylbenzene,
(g) vinyl compounds having a heterocyclic ring such as triallyl isocyanurate, triallyl cyanurate, vinylpyridine,
(h) In addition, one or more kinds of vinyl cyanide compounds such as (meth) acrylonitrile or α-chloroacrylonitrile, acrolein, formylsterol, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone and the like can be mentioned.

The ester of unsaturated carboxylic acids (c) is preferably an ester of monocarboxylic acids.
Examples of esters of monocarboxylic acids include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meta ) Acrylate, n-pentyl (meth) acrylate, i-pentyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl ( (Meth) acrylate, i-nonyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, etc. ) Alkyl esters of acrylic acid;
Aminoalkyl esters of (meth) acrylic acid such as aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, butylaminoethyl (meth) acrylate;
(Meth) acrylates having an aromatic ring such as benzyl (meth) acrylate, benzoyl (meth) acrylate, allyl (meth) acrylate;
(Meth) acrylates having an epoxy group such as glycidyl (meth) acrylate, metaglycidyl (meth) acrylate, and epoxycyclohexyl (meth) acrylate;
(Meth) acrylates having various functional groups such as N-methylol (meth) acrylamide, γ- (meth) acryloxypropyltrimethoxysilane, tetrahydrofurfuryl methacrylate;
Polyfunctional (meth) acrylates such as ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene dimethacrylate (EDMA), polyethylene glycol dimethacrylate, isobutylene ethylene dimethacrylate;
1 type, or 2 or more types, etc. are mentioned.

The rubber composition containing each component demonstrated above can be prepared similarly to the past. That is, first a rubber component is blended at a predetermined ratio and kneaded, then an additive other than a foaming component and a crosslinking component is added and kneaded, and finally a foaming component and a crosslinking component are added and kneaded to form a rubber composition. A thing is obtained. For kneading, for example, a kneader, a Banbury mixer, an extruder, or the like can be used.
<Image forming apparatus>
The image forming apparatus of the present invention is characterized by incorporating the conductive foam rubber roller 1 of the present invention. Examples of the image forming apparatus of the present invention include various image forming apparatuses using electrophotography such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, or a complex machine of these.

<Example 1>
(Preparation of rubber composition)
As rubber, 10 parts by mass of ECO [HYDRIN (registered trademark) T3108 manufactured by Nippon Zeon Co., Ltd.], 10 parts by mass of EPDM (registered trademark EPDM505A manufactured by Sumitomo Chemical Co., Ltd.), and NBR [JSR Co., Ltd.] ) JSR N250 SL, non-oil-extended, low nitrile NBR, acrylonitrile content: 20%], 80 parts by mass.

  And each component shown in following Table 1 was mix | blended with 100 mass parts of these rubber | gum total amounts, and it knead | mixed for 3 to 5 minutes at 80 degreeC using the closed kneader, and prepared the rubber composition.

Each component in Table 1 is as follows. In addition, the mass part in a table | surface is the quantity per 100 mass parts of total amounts of rubber | gum.
Filler: Carbon black HAF [trade name Seast 3 manufactured by Tokai Carbon Co., Ltd.]
Foaming agent: ADCA-based foaming agent (trade name Binhore AC # 3 manufactured by Eiwa Chemical Industry Co., Ltd.)
Acid acceptor: Hydrotalcite [DHT-4A-2 manufactured by Kyowa Chemical Industry Co., Ltd.]
Cross-linking agent: Powdered sulfur [manufactured by Tsurumi Chemical Co., Ltd.]
Accelerator DM: Di-2-benzothiazyl disulfide [Noxer (registered trademark) DM manufactured by Ouchi Shinsei Chemical Co., Ltd.]
Accelerator TS: Tetramethylthiuram disulfide [Noxeller TS manufactured by Ouchi Shinsei Chemical Co., Ltd.]
Acceleration aid: Zinc oxide [manufactured by Hakusuitec Co., Ltd.]
(Adjustment of base and core)
4 and 5, the pressing amount by the fixing mechanism in four directions (not shown) of the base 14 (the inner diameter of the opening 13: 10.5 mm) and the core 16 (the outer diameter of the cross section 15: 3.5 mm) is applied. 4 corresponds to the direction of the fixing mechanism, the maximum and minimum values of vertical and horizontal in four directions of the distance d ₁ to d ₄ of the shaft 17, and adjusted so that the error obtained by the equation (1) is 30%.

(Manufacture of conductive foam rubber roller)
The previous rubber composition is supplied to the extruder 6 of the manufacturing apparatus 5 shown in FIG. 1, and the extruder 6 is operated so that the annular shape between the base 14 and the core 16 whose error has been adjusted as described above is adjusted. Extruded into a cylindrical shape with an outer diameter of 10.5 mm and an inner diameter of 3.5 mm through the gap, and the extruded cylindrical body 7 is continuously cut out without being cut. By continuously passing through the cross-linking device 9, cross-linking and foaming were continuously performed.

The output of the microwave cross-linking apparatus 8 was 8 kW, the control temperature in the tank was 160 ° C., the control temperature in the tank of the hot air cross-linking apparatus 9 was 250 ° C., and the effective length of the heating tank was 8 m.
When the cylindrical body 7 immediately after passing through the hot-air bridging device 9 was cut and the uneven thickness was measured, it was 1.30.
Next, after foaming and crosslinking, the cooled cylindrical body 7 is cut into a length of 220 mm to produce a conductive foamed rubber roller 1, and then subjected to secondary crosslinking by heating in a hot air oven at 160 ° C. for 1 hour. A metal (SUM-24L) shaft 3 having an outer diameter of φ6 mm is press-fitted into the through hole 2 to be electrically connected and mechanically fixed, and then the outer diameter becomes φ12 mm using a cylindrical grinder. The outer peripheral surface 4 was traverse-polished.

<Example 2>
4 and 5, the pressing amount by the fixing mechanism in four directions (not shown) of the base 14 (the inner diameter of the opening 13: 10.5 mm) and the core 16 (the outer diameter of the cross section 15: 3.5 mm) is applied. 4 corresponds to the direction of the fixing mechanism, the maximum value and the minimum value of the four directions of the distance d ₁ to d ₄ of the shaft 17, an error obtained by the equation (1) was adjusted to 20% A conductive foam rubber roller 1 was produced in the same manner as in Example 1 except for the above.

It was 1.20 when the cylindrical body 7 just after passing the hot-air bridge | crosslinking apparatus 9 was cut, and the thickness deviation was measured.
<Example 3>
As a rubber component, 10 parts by mass of ECO, 10 parts by mass of EPDM, and 40 parts by mass of NBR are further blended with 40 parts by mass of SBR (JSR 1502, JSR 1502, non-oil-extended), and the base shown in FIGS. 14 (the inner diameter of the opening 13: 10.5 mm) and the pressing amount of the center core 16 (outer diameter of the cross section 15: 3.5 mm) by a four-direction fixing mechanism (not shown) correspond to the four-direction fixing mechanism. , the maximum and minimum values of the four directions of the distance d ₁ to d ₄ of the shaft 17, except that the error obtained by the equation (1) was adjusted to 25% in the same manner as in example 1 Thus, the conductive foam rubber roller 1 was manufactured.

It was 1.26 when the cylindrical body 7 just after passing the hot-air bridge | crosslinking apparatus 9 was cut, and the thickness deviation was measured.
<Example 4>
As rubber, 10 parts by mass of ECO, 10 parts by mass of EPDM, and 80 parts by mass of SBR were blended, and the base 14 (inner diameter of the opening 13: 10.5 mm) shown in FIGS. 4 and 5 and the core 16 (outside of the cross section 15) diameter: of 3.5 mm), the push amount of the four directions of the fixing mechanism (not shown) corresponding to such four directions of the fixing mechanism, the maximum value and the minimum in the distance d ₁ to d ₄ four directions of the shaft 17 A conductive foam rubber roller 1 was produced in the same manner as in Example 1 except that the error was adjusted so as to be 30% based on the value from Equation (1).

When the cylindrical body 7 immediately after passing through the hot-air bridging device 9 was cut and the uneven thickness was measured, it was 1.30.
<Comparative example 1>
4 and 5, the pressing amount by the fixing mechanism in four directions (not shown) of the base 14 (the inner diameter of the opening 13: 10.5 mm) and the core 16 (the outer diameter of the cross section 15: 3.5 mm) is applied. 4 corresponds to the direction of the fixing mechanism, the maximum value and the minimum value of the four directions of the distance d ₁ to d ₄ of the shaft 17, an error obtained by the equation (1) was adjusted to 35% A conductive foam rubber roller 1 was produced in the same manner as in Example 1 except for the above.

It was 1.34 when the cylindrical body 7 just after passing the hot air bridge | crosslinking apparatus 9 was cut, and the thickness deviation was measured.
<Comparative example 2>
4 and 5, the pressing amount by the fixing mechanism in four directions (not shown) of the base 14 (the inner diameter of the opening 13: 10.5 mm) and the core 16 (the outer diameter of the cross section 15: 3.5 mm) is applied. 4 corresponds to the direction of the fixing mechanism, the maximum value and the minimum value of the four directions of the distance d ₁ to d ₄ of the shaft 17, an error obtained by the equation (1) was adjusted to 40% A conductive foam rubber roller 1 was produced in the same manner as in Example 3 except for the above.

The cylindrical body 7 immediately after passing through the hot air bridging device 9 was cut and the uneven thickness was measured and found to be 1.40.
<Comparative Example 3>
4 and 5, the pressing amount by the fixing mechanism in four directions (not shown) of the base 14 (the inner diameter of the opening 13: 10.5 mm) and the core 16 (the outer diameter of the cross section 15: 3.5 mm) is applied. 4 corresponds to the direction of the fixing mechanism, the maximum and minimum values of vertical and horizontal in four directions of the distance d ₁ to d ₄ of the shaft 17, an error obtained by the equation (1) was adjusted to 38% A conductive foam rubber roller 1 was produced in the same manner as in Example 4 except for the above.

It was 1.38 when the cylindrical body 7 just after passing the hot-air bridge | crosslinking apparatus 9 was cut, and the uneven thickness degree was measured.
<Check for cracks>
In each example and comparative example, after cutting to a predetermined length, the conductive foamed rubber roller 1 before secondary cross-linking is cut so as to be divided into eight in the circumferential direction along the axial direction, and the cut surface is cracked. The presence or absence was confirmed.

  The results are shown in Table 2.

From the results of Examples 1 to 4 and Comparative Examples 1 to 3 in Table 2, because the thickness of the cylindrical body 7 immediately after passing through the hot-air bridging device 9 is 1.3 or less, there are no cracks inside. It has been found that a conductive foam rubber roller that does not cause peeling or dents in the subsequent polishing step can be produced.
From the results of the examples and comparative examples, the cylindrical body 7 immediately after passing through the hot-air bridging device 9 when the cylindrical body 7 is extruded by combining the base 14 and the core 16 shown in FIGS. 4 and 5. in order to the thickness deviation 1.3 or less, the press amount of the four directions of the fixing mechanism, not shown, corresponding to such four directions of the fixing mechanism, four directions of the distance d ₁ to d ₄ of the shaft 17 From the maximum value and the minimum value, it was found that the error calculated by the equation (1) is preferably 10% or less.

DESCRIPTION OF SYMBOLS 1 Conductive foaming rubber roller 2 Through-hole 3 Shaft 4 Outer peripheral surface 5 Manufacturing apparatus 6 Extruder 7 Cylindrical body 8 Microwave bridge | crosslinking apparatus 9 Hot-air bridge | crosslinking apparatus 10 Take-out machine 11 Through-hole 12 Outer peripheral surface 13 Opening 14 Base 15 Cross section 16 Core 17 axis 18 vertex d _{1 to} d ₄ distance E extrusion direction T _max maximum thickness T _min minimum thickness

Claims (4)

A rubber composition having electrical conductivity, crosslinkability, and foamability is continuously extruded into a cylindrical shape, and then the extruded cylindrical body is kept long without being cut. A manufacturing method for producing a conductive foamed rubber roller through a step of continuously foaming and cross-linking by passing through an apparatus, wherein in the step, a maximum radial thickness T _{max of} a cross section immediately after passing through a hot-air cross-linking device minimum thickness as thickness deviation, expressed by the ratio T _{max /} T _min and T _min is 1.3 or less, the rubber composition of the extrusion, foaming, and conductive, characterized in that crosslinking and Manufacturing method of foam rubber roller. For the extrusion molding, an extruder having a die whose opening shape is circular and a core disposed in the die and having a circular cross-sectional shape in the same plane as the opening of the die is used. A maximum value and a minimum value of the radial distance between the opening of the base and the center of the core at a plurality of locations in the circumferential direction of the opening, From equation (1):

The rubber composition is extruded into a cylindrical shape through an annular gap between the base and the core while the base and the core are aligned so that the error required by the step is within 10%. The method for producing a conductive foamed rubber roller according to claim 1 to be molded.   A conductive foam rubber roller manufactured by the manufacturing method according to claim 1.   4. An image forming apparatus comprising the conductive foam rubber roller according to claim 3.

Images